Desublimation cold box
UF₆ cold boxes for desublimation.
Withdrawal stations that turn UF₆ gas straight to solid inside the cylinder, filling it at low pressure.
Explore the components
How it works
From gas to solid, inside the cylinder
Uranium hexafluoride gas that meets a surface colder than its sublimation temperature, 56.5 °C (134 °F) at atmospheric pressure, freezes straight onto it as a solid. It never becomes a liquid unless it is above its triple point, about 64 °C (147 °F) and 1.5 atm.
An ASC cold box, also called a withdrawal station, uses that to fill cylinders. It chills the cylinder with refrigerated air, and UF₆ gas arriving through the valve builds up as solid on the cold wall, keeping the cylinder at low pressure as it fills.
- Desublimes below
- 56.5 °C (134 °F) at 1 atm
- Triple point
- 64 °C (147 °F) at about 1.5 atm (22 psia)
- Cylinders
- 30- and 48-series, plus smaller cylinders on a compact model
- Cooling
- Packaged refrigeration, circulating air
The cycle
Four steps from load to unload
Load the cylinder
A transporter rolls an empty or partly filled cylinder in on its stillage onto the weigh frame, and the heat-traced pigtail is connected.
Purge and chill
With the door closed and locked, a dry-air purge clears moist air from the enclosure, then chilled air circulates round the cylinder.
Collect the UF₆
Gas entering through the valve desublimes on the cold wall, building up as solid, while the weigh frame tracks the fill.
Close out the cycle
At the target weight the valve closes, the pigtail is disconnected, and the cylinder rolls out on its stillage for storage or shipment.
Design
Built for safe, steady filling
Every cold box is engineered with the same expertise as ASC pressure vessels and autoclaves.
Gas to solid, never liquid
Chilling the cylinder means incoming UF₆ freezes directly onto the wall. There is no liquid in the cylinder and it fills at low pressure.
Cooling from underneath
A fan at the rear drives air through the evaporator coil and forward through a duct in the floor, so it rises round the cylinder from directly beneath it. Airflow is checked with CFD.
Packaged refrigeration
Compressors and condensers are built into the rear of the box, with variable-speed control to hold temperature as the load changes during a fill.
Weighed in place
The cylinder sits on a weigh frame with load cells, so the station tracks every fill to its target weight.
Safe by design
An interlocked door stays locked while the box runs, with a release inside. A dry-air purge limits condensation, and the pigtail is heat traced and interlocked.
Self-contained
Controls, power, and refrigeration ship mounted and pre-wired on the box. CPC runs the cycle from a swing-arm operator screen and records every run.
FAQ
Cold box questions
What is a UF₆ cold box?
A cold box, also called a withdrawal station, is a refrigerated enclosure for a UF₆ cylinder. It chills the cylinder with circulating air so uranium hexafluoride gas entering it desublimes, turning directly to solid on the cylinder wall.
What is desublimation?
Desublimation is the reverse of sublimation: a gas turning straight to a solid without passing through a liquid. Below its triple point, about 64 °C and 1.5 atm, UF₆ gas that meets a cold surface does exactly that.
Where are cold boxes used?
Cold boxes collect UF₆ from enrichment and other processes and fill cylinders for storage or shipment. Paired with a hot box, they move UF₆ from one cylinder to another without melting it.
Which cylinders can an ASC cold box hold?
ASC cold boxes are built for standard 30- and 48-series UF₆ cylinders, including 30B, 30C, 48X, 48Y, and 48G, with interchangeable stillages. Smaller cylinders such as the 5B have their own compact model.
Contact
Plan your cold box.
Tell us your cylinders, fill rates, and facility layout. Our engineers will size a cold box and its refrigeration.